JERUSALEM (CNN) -- Six people were killed and more than 60 were injured Thursday when an explosion ripped through a senior Hamas commander's house in northern Gaza, Palestinian security sources said.

The blast happened at a house belonging to Ahmed Hamudi, a senior Hamas commander, Palestinian security and medical sources said.

Eyewitnesses called it a "work accident."

The Israel Defense Forces said it was not involved, calling the incident an internal Palestinian matter.

Earlier Thursday in northern Gaza, the IDF said it shot two militants placing explosives near a border fence. The two were killed, according to sources from the Democratic Front for the Liberation of Palestine and Fatah.

Meanwhile, Israel also reported another barrage of rockets fired into the Jewish state from Gaza. A 59-year-old woman was injured when a rocket landed in a house in Yad Mordechai.

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Militants in Gaza have launched more than 2,300 mortars and rockets since the start of 2008, while 2,000 were fired in all of 2007, according to the Israeli military.

The Israeli military responds to the attacks by carrying out airstrikes and ground operations targeting militants in Gaza. The reprisals often lead to civilian casualties, inflaming the Palestinian leadership.

Egypt has been trying to broker a peace deal between Israel and Gaza's Hamas leaders because Israel will not directly negotiate with the hard-line Islamic group.

The U.S. and Israel consider Hamas a terrorist outfit because it does not recognize the Jewish state's right to exist. The group also refuses to renounce terrorism.

Hamas seized control of Gaza last year after routing security forces belonging to Palestinian Authority President Mahmoud Abbas' Fatah movement.

Palestinians elected a Hamas-led Palestinian Authority government in a U.S.-backed vote in 2006.